This invention relates to an embossed type separator suitable for use in lead-acid storage batteries.
With the decrease in size and weight of storage batteries, the separator used hitherto has measured 0.5 mm or less in thickness, so that it has been usual to use it in combination with a glass mat in layers or to provide it with ribs in order to provide a space of 1 mm or more between the positive plate and the negative plate of the cell of the battery. However, this type of separator is defective in that such a combination is troublesome and attachment of the ribs thereto involves a waste of additional time and labor, resulting in a rise in manufacturing cost. In order to avoid these disadvantages, there has been proposed a type of thin separator embossed to form long ribs extending in the vertical direction in order to increase its apparent thickness so that it has become unnecessary to use the separate glass mat in combination with the separator or to attach ribs thereto. This separator, however, has the disadvantage that it cannot withstand the pressure from the positive plate and the negative plate of a cell of a storage battery, and therefore it is liable to be deformed. In addition, it has to be used in such a condition that its ribs may be positioned to extend vertically in order to take into consideration the discharge of gases which are passed therethrough.
There has also been known an embossed type of separator having a large number of large and small embossed projections. However, this embossed type of separator is inconvenient in that, since the concave and convex forms of both surfaces are different from one another, when they are interposed between a positive plate and a negative plate, special care has to be taken so that its right side surfaces may face the right plates, respectively, and thus the use thereof is troublesome. This also causes difficulty in the discharging of gases. Furthermore, since they are made by embossing on the same side surface a large number of small projections in the form of a V-shape in section, the top portion of the small projections are formed by being given especially a sudden deformation by pincer pressure applied from both sides of the separator during embossing, and this often results in cracks or breaks on the top portions thereof, and a production loss results.